A number of processes have been studied and patented for the removal of toxic or otherwise offending substances from tobacco and like stimulants. It is known, for example, to extract nicotine from tobacco with solvents such as ammonia, ethylene oxide and the like. These and similar processes have not attained general acceptance due to the fact that the extraction solvents are not sufficiently selective and remove not only the nicotine, but varying amounts of the desirable constituents associated with the pleasant aroma of tobacco.
The use of condensed gases has been studied quite extensively because of the known selective dissolving capacity of these substituents. The use of liquid SO.sub.2 has been described in German Patent No. 558,351, wherein a process for removing nicotine from tobacco is disclosed. This extraction solvent has not attained any appreciable acceptance due to the fact that SO.sub.2 is not sufficiently selective, may generate toxic residues and is highly corrosive to the apparatus employed.
Accordingly, the art has long concerned itself with the problem of selective extraction of nicotine from tobacco with nontoxic solvents which do not corrode the apparatus employed.